The present invention relates to catalysts for the polymerisation of olefins. In particular, it relates to high activity catalysts for the polymerisation of olefins obtained from cyclopentadienyl compounds of a transition metal, organometallic aluminium compounds and water.
The invention also relates to processes for the polymerisation of olefins carried out in the presence of the catalysts of the invention.
Homogeneous catalytic systems based on metallocene compounds, aluminium alkyl compounds and water are known to be active in the polymerisation of olefins.
In European Patent Application EP 384,171, catalysts for the polymerisation of olefins are described which comprise the reaction product of:
(a) a metallocene compound of formula:
(C5Rxe2x80x2n)mRxe2x80x3p(C5Rxe2x80x2n)MX3xe2x88x92m
wherein (C5Rxe2x80x2n) is an optionally substituted cyclopentadienyl group and two or four Rxe2x80x2 substituents of one and the same cyclopentadienyl group can form one or two rings having 4 to 6 carbon atoms; Rxe2x80x3 is a divalent radical bridging the two cyclopentadienyl groups; X can be for instance an halogen atom; M is a transition metal selected from Ti, Zr and Hf; p is 0 or 1; m is 0, 1 or 2, and when m=0 then p=0, and when p=0 at least one Rxe2x80x2 substituent is different from hydrogen; n=4 when p=1, and n=5 when p=0; and
(b) an alumoxane of the formula: 
wherein the substituents R can generically be alkyl, alkenyl or alkylaryl radicals, having 2-20 carbon atoms.
The alumoxanes (b) are prepared by reacting the corresponding trialkylaluminium compounds with water in a molar ratio of 2:1. In the alumoxanes used in the embodiment examples, the R substituents are isobutyl or 2-methylpentyl groups.
European Patent Application EP 575,875 describes homogeneous catalytic systems for the polymerisation of olefins comprising:
(A) a cyclopentadienyl compound of formula:
(C5R1xxe2x88x92mH5xe2x88x92x)R2m(C5R1yxe2x88x92mH5xe2x88x92y)nMQ3xe2x88x92n
in which M is Ti, Zr or Hf; C5R1xxe2x88x92mH5xe2x88x92x and C5R1yxe2x88x92mH5xe2x88x92y are equally or differently substituted cyclopentadienyl rings and two or four substituents R1 of the same cyclopentadienyl group can form one or two rings, having from 4 to 6 carbon atoms; R2 is a bridging group which links the two cyclopentadienyl rings; the substituents Q are preferably chlorine atoms; m can be 0 or 1; n can be 0 or 1, being 1 when m=1; x is an integer comprised between m+1 and 5; y is an integer comprised between m and 5;
(B) an organometallic aluminium compound of formula:
AlR43xe2x88x92zHz
wherein the substituents R4 are alkyl, alkenyl or alkylaryl radicals, containing from 1 to 10 carbon atoms, which may also contain Si or Ge atoms, at least one of the substituents R4 being different from a straight alkyl group; z is 0 or 1; and
(C) water.
The molar ratio between the organometallic aluminium compound and the water is comprised between 1:1 and 100:1. In the embodiment examples, only triisobutylaluminium and triisohexylaluminium are used as the organometallic aluminium compounds.
International Patent Application WO 96/02580 describes improved catalytic systems comprising:
(A) a cyclopentadienyl compound of formula:
(C5R1xxe2x88x92mH5xe2x88x92x)R2m(C5R1yxe2x88x92mH5xe2x88x92y)nMQ3xe2x88x92n
in which M is Ti, Zr or Hf; C5R1xxe2x88x92mH5xe2x88x92x and C5R1yxe2x88x92mH5xe2x88x92y are equally or differently substituted cyclopentadienyl rings; the substituents R1, the same or different from each other, are alkyl, alkenyl, aryl, alkylaryl or arylalkyl radicals, which have 1 to 20 carbon atoms, optionally containing Si or Ge atoms or groups Si(CH3)3, or two or four substituents R1 of one and the same cyclopentadienyl group can also form one or two rings, having 4 to 6 carbon atoms; R2 is a bridging group linking the two cyclopentadienyl rings and is selected from CR32, C2R34, SiR32, Si2R34, GeR32, Ge2R34, R32SiCR32, NR1 and PR1, wherein the substituents R3, the same or different from each other, are R1 or hydrogen, or two or four substituents R3 can also form one or two rings, having 3 to 6 carbon atoms; the substituents Q, the same or different from each other, are halogen, hydrogen, R1, OR1, SR1, NR12 or PR12; m can be 0 or 1; n can be 0 or 1, being 1, if m=1; x is an integer comprised between (m+1) and 5; and y is an integer comprised between m and 5;
(B) an organometallic aluminium compound of formula:
Al(CH2xe2x80x94CR4R5R6)wR7yHz
wherein in the (CH2xe2x80x94CR4R5R6) groups, the same or different from each other, R4 is an alkyl, alkenyl or arylalkyl group, having from 1 to 10 carbon atoms; R5 is an alkyl, alkenyl, aryl, arylalkyl or alkylaryl group, having from 3 to 50 carbon atoms which is different from a straight alkyl or alkenyl group and, optionally, R4 and R5 fused together can form a ring, having from 4 to 6 carbon atoms; R6 is hydrogen or an alkyl, alkenyl or arylalkyl group, having from 1 to 10 carbon atoms; the R7 substituents, the same or different from each other, are alkyl, alkenyl, aryl, arylalkyl or alkylarl radicals. containing from 1 to 10 carbon atoms, optionally containing Si or Ge atoms; w is 1, 2 or 3; z is 0 or 1; y=3xe2x88x92wxe2x88x92z; and
(C) water.
The molar ratio between the organometallic aluminium compound and water is comprised between 1:1 and 100:1. The only organometallic aluminium compounds disclosed are those wherein the (CH2xe2x80x94CR4R5R6) groups are 2,4,4-trimethyl-pentyl, 2-phenyl-propyl or 1-butene oligomers. According to the cited application, the compound (B) can be contacted with (A) and successively with (C), or can be reacted with (C) and successively with (A); moreover, in the examples, the three components are mixed together at the same time.
It has now surprisingly been found that, by contacting components (A), (B) and (C) described in the above-mentioned European patent application EP 575,875 according to a novel procedure, catalysts can be obtained with higher activity than those obtained according to the prior art.
It is therefore an object of the present invention a catalyst for the polymerisation of olefins, comprising the product obtainable by contacting the following components:
(A) a cyclopentadienyl compound of formula (I):
(C5R1xxe2x88x92mH5xe2x88x92x)R2m(C5R1yxe2x88x92mH5xe2x88x92y)nMQ3xe2x88x92nxe2x80x83xe2x80x83(I)
wherein M is a metal selected from the group consisting of Ti, Zr and Hf; C5R1xxe2x88x92mH5xe2x88x92x and C5R1yxe2x88x92mH5xe2x88x92y are equally or differently substituted cycopentadienyl rings; the substituents R1, the same or different from each other, are selected from the group consisting of a linear or branched, saturated or unsaturated C1-C20 alkyl, C6-C20 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl groups radicals, optionally containing one or more atoms belonging to groups 13-16 of the Periodic Table of the Elements (new IUPAC notation), such as B, P, Al, Si, Ge, O and S atoms, or two or four substituents R1 of the same cyclopentadienyl group form one or two rings, having 4 to 6 carbon atoms; R2 is a bridging group between the two cyclopentadienyl rings and is selected from the group consisting of CR32, C2R34, SiR32, Si2R34, GeR32, Ge2R34, R32SiCR32, NR1 and PR1, wherein the substituents R3, the same or different from each other, are hydrogen or have the same meaning of R1, or two or four substituents R3 form one or two rings, having 3 to 6 carbon atoms, the substituents Q, the same or different from each other, are selected from the group consisting of hydrogen, halogen, OH, SH, R1, OR1, SR1, NR12 and PR12; m is 0 or 1; n is 0 or 1, being 1 when m=1; x ranges from (m+1) to 5, and preferably between (m+2) and 5; and y ranges from m to 5;
(B) one or more organometallic aluminium compounds of formula (II):
AlR43xe2x88x92zHzxe2x80x83xe2x80x83(II)
wherein the substituents R4, the same or different from each other, are linear or branched, saturated or unsaturated C1-C20 alkyl or C7-C20 alkylaryl radicals, optionally containing Si or Ge atoms, at least one of the substituents R4 being different from a straight alkyl group; z is 0 or 1; and
(C) water;
xe2x80x83the molar ratio between said organometallic aluminium compound (B) and water (C) is comprised between 1:1 and 100:1, preferably between 1:1 and 50:1, and more preferably is 2:1; said catalyst being obtainable by a process comprising the following steps:
(i) contacting component (A) with part of component (B), in the absence of component (C);
(ii) contacting part of component (B) with component (C), in the absence of component (A); and successively
(iii) contacting the products obtained in steps (i) and (ii);
wherein the components (B) used in steps (i) and (ii) can be the same or different from each other.
In the cyclopentadienyl compounds of formula (I), M is preferably zirconium. When m=0 in formula (I), C5R1xxe2x88x92mH5xe2x88x92x and C5R1yxe2x88x92mH5xe2x88x92y are preferably pentamethyl-cyclopentadienyl, indenyl or 4,5,6,7-tetrahydroindenyl groups; the Q substituents are preferably chlorine atoms or C1-C7 hydrocarbon groups, and more preferably are methyl groups.
Non-limiting examples of cyclopentadienyl compounds of formula (I), wherein m=0, are:
wherein Me=methyl, Et=ethyl, Cp=cyclopentadienyl, Ind=indenyl, H4Ind=4,5,6,7-tetrahydroindenyl and Benz=benzyl.
When m=1 in formula (I), C5R1xxe2x88x92mH5xe2x88x92x and C5R1yxe2x88x92mH5xe2x88x92y are preferably tetramethyl-cyclopentadienyl, indenyl, 4,5,6,7-tetrahydroindenyl, 2-methyl-4,5,6,7-tetrahydroindenyl, 4,7-dimethyl-4,5,6,7-tetrahydroindenyl, 2,4,7-trimethyl-4,5,6,7-tetrahydroindenyl or fluorenyl groups; R2 preferably (CH3)2Si less than  or xe2x80x94CH2CH2xe2x80x94; the Q substituents are preferably chlorine atoms or C1-C7 hydrocarbon groups, and more preferably methyl groups.
Non-limiting examples of cyclopentadienyl compounds of formula (I), wherein m=1, are:
wherein Me=methyl, Cp=cyclopentadienyl, Ind=indenyl, Flu=fluorenyl, Ph=phenyl and H4Ind=4,5,6,7-tetrahydroindenyl.
In component (B) of the catalyst of the invention, according to a preferred embodiment, said organometallic aluminium compounds have formula (III):
Al(CH2xe2x80x94CR4R5R6)wR7yHzxe2x80x83xe2x80x83(III)
wherein in the (CH2xe2x80x94CR4R5R6) groups, the same or different from each other, R4 is a linear or branched, saturated or unsaturated C1-C10 alkyl or C7-C10 arylalkyl group; R5 is a saturated or unsaturated C3-C50 alkyl, C6-C50 aryl, C7-C50 arylalkyl or alkylaryl group, which is different from a straight alkyl or alkenyl group; or R4 and R5 form a ring, having from 4 to 6 carbon atoms; R6 is hydrogen or a linear or branched, saturated or unsaturated C1-C10 alkyl, C7-C10 arylalkyl group; the R7 substituents, the same or different from each other, are linear or branched, saturated or unsaturated C1-C10 alkyl, C6-C10 aryl, C7-C10 arylalkyl or alkylaryl groups, optionally containing Si or Ge atoms; w is 1, 2 or 3; z is 0 or 1; and y=3xe2x88x92wxe2x88x92z.
A particularly preferred compound corresponding to formula (III) is tris(2,4,4-trimethyl-pentyl)aluminium (TIOA).
According to another preferred embodiment of the catalyst of the invention, said organometallic aluminium compounds, to be used as component (B), correspond to formula (IV):
Al(CH2xe2x80x94CR4R5xe2x80x94CR6R7R8)wR9qHzxe2x80x83xe2x80x83(IV)
wherein R4 is a linear or branched, saturated or unsaturated C1-C10 alkyl or C7-C10 arylalkyl group; R5 is hydrogen or a linear or branched, saturated or unsaturated C1-C10 alkyl or C7-C10 arylalkyl group; R6 and R7, the same or different from each other, are linear or branched, saturated or unsaturated C1-C10 alkyl, C6-C10 aryl, C7-C10 arylalkyl or alkylaryl groups; R8 is hydrogen or a linear or branched, saturated or unsaturated C1-C10 alkyl, C6-C10 aryl, C7-C10 arylalkyl or alkylaryl group; R9 is a linear or branched, saturated or unsaturated C1-C10 alkyl or C7-C10 arylalkyl group; a carbon atom in the compound of formula (IV) being optionally replaced by a Si or Ge atom; w is 1, 2 or 3; z is 0 or 1; and q=3xe2x88x92wxe2x88x92z.
Particularly preferred compounds corresponding to formula (IV) are tris(2,3,3-trimethyl-butyl)aluminium (TTMBA) and tris(2,3-dimethyl-butyl)aluminium (TDMBA).
The molar ratio between said organometallic aluminium compound (component B) and said cyclopentadienyl compound (component C) is preferably comprised between 50 and 50,000, and more preferably between 500 and 5,000.
According to the invention, both in step (i) and (ii), component (B) can suitably comprise a mixture of two or more organometallic aluminum compounds of formula (II), and preferably of compounds of formula (III) and/or (IV).
Moreover, both in steps (i) and (ii), component (B) can be used in combination with organometallic aluminum compounds other than those of formulae (II), (III) and (IV), or in mixture with other compatible cocatalysts known in the state of the art. In the organometallic aluminium compounds of formulae (II), (III) or (IV), z is 0 or 1. As it is known in the state of the art, aluminium trialkyls may contain small amounts of dialkyl-aluminium hydride; the hydride content can slightly change during prolonged storage periods and depending on the storage temperature. Therefore, according to a preferred embodiment of the invention, component (B) is a mixture of the two organometallic aluminium compounds of formula (II), (III) and/or (IV) wherein z=0 and z=1, so that the molar ratio between the hydrogen atoms directly bound to aluminium and aluminium atoms (i.e. the overall z value) is lower than 0.8, and even more preferably ranges from 0.02 to 0.3. Mixtures of organometallic aluminium compounds having said overall z values can be prepared with methods known in the state of the art, for instance by mixing the corresponding trialkylaluminium and dialkylaluminium hydride in appropriate molar ratios.
Another object of the present invention is a process for the preparation of a catalyst as described above, said process comprising the following steps:
(i) contacting component (A) with part of component (B) in the absence of component (C);
(ii) contacting part of component (B) with component (C) in the absence of component (A); and successively
(iii) contacting the products obtained in steps (i) and (ii);
wherein the components (B) used in steps (i) and (ii) can be the same or different from each other.
In step (i), component (A) is preferably contacted with component (B) in a suitable solvent, such as toluene; the concentration of component (A) in said solution is preferably comprised between 10xe2x88x922 and 10xe2x88x928 mol/l. The amount of component (B) used in step (i) preferably ranges from 1 to 80% mol of the total amount of (B) used in the process of the invention, and more preferably from 2 to 10% mol. The precontact can be carried out in the presence of small amounts of monomer. The contact time is generally comprised between 1 and 60 minutes, prefer-ably between 5 and 20 minutes.
In step (ii) of the process of the invention, according to a particular embodiment of the invention, water can be gradually added to component (B) in solution, in an aliphatic or aromatic inert hydrocarbon solvent, such as heptane or toluene. In said solution, the concentration of the product obtainable by contacting said organometallic aluminium compound and water is preferably comprised between 10 and 10xe2x88x923 mol/l. The amount of component (B) used in step (ii) preferably ranges from 20 to 99% mol of the total amount of (B) used in the process of the invention, and more preferably from 90 to 98% mol.
According to another embodiment, the water can be introduced in the monomer or in one of the monomers to be polymerised, and contacted with said organometallic alunminium compound. According to still another embodiment, the water can be reacted in a combined form, as a hydrated salt, or it can be adsorbed or absorbed on an inert support such as silica. The contact time is generally comprised between 1 and 60 minutes, prefer-ably between 5 and 20 minutes.
The catalysts of the present invention can be used on inert supports, such as silica, alumina, styrene/divinylbenzene copolymers, homopolymers and copolymers of ethylene and xcex1-olefins; the thus obtained solid systems can be suitably used in gas phase polymerizations.
The catalysts of the present invention can be used in the polymerisation reactions of olefins. Therefore, according to further object, the invention provides a process for the polymerisation of an olefin carried out in the presence of a catalyst as described above.
Olefins which can be polymerised with the process of the present invention are, for instance, xcex1-olefins of formula CH2xe2x95x90CHR, wherein R is hydrogen or a C1-C20 alkyl radical.
The catalysts according to the present invention can conveniently be used in ethylene homopolymerization, in particular for the preparation of HDPE, and in ethylene copolymerization, in particular for the preparation of LLDPE. In ethylene polymerisation, according to a preferred embodiment of the invention, component (B) is a mixture of the two organometallic aluminium compounds of formula (II) wherein z=0 and z=1, in such amounts that the molar ratio between the hydrogen atoms directly bound to aluminium and aluminium atoms (i.e. the overall z value) preferably ranges from 0.02 to 0.3. More specifically, in step (i), said overall z value is preferably higher than 0.02, and more preferably is about 0.09; in step (ii), said overall z value is preferably lower than 0.2.
The process according to the present invention allow to prepare LLDPE copolymers having a content of ethylene units of between 80 and 99 mol %; said copolymers have a density comprised between 0.87 and 0.95 g/cm3 and are characterised by a uniform distribution of the xcex1-olefin units along the polymeric chain.
Comonomers which can be suitably used in ethylene copolymers comprise xcex1-olefins of formula CH2xe2x95x90CHR, wherein R is a linear, branched or cyclic C1-C20 alkyl, and cycloolefins. Examples of such olefins are propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, allylcyclohexane, cyclopentene, cyclohexene, norbornene and 4,6-dimethyl-1-heptene. The units deriving from the olefins of formula CH2xe2x95x90CHR or from cycloolefins are generally present in the copolymers in a quantity ranging from 1 to 20 mol %.
The copolymers can also contain units deriving from polyenes, in particular from conjugated or non-conjugated, linear or cyclic dienes, such as 1,4-hexadiene, isoprene, 1,3-butadiene, 1,5-hexadiene and 1,6-heptadiene.
According to another object of the invention, the above catalysts can be used in propylene homopolymerization, in particular for the production of isotactic polypropylene.
In propylene polymerisation, according to a preferred embodiment of the invention, component (B) is a mixture of the two organometallic aluminium compounds of formula (II) wherein z=0 and z=1, in such amounts that the molar ratio between the hydrogen atoms directly bound to aluminium and aluminium atoms (i.e. the overall z value) preferably ranges from 0.02 to 0.3. More specifically, in step (i), said overall z value is preferably higher than 0.02, and more preferably is about 0.09; in step (ii), said overall z value is preferably lower than 0.4.
According to a further embodiment, the catalysts of the invention can be advantageously used in the preparation of elastomeric copolymers of ethylene with xcex1-olefins of formula CH2xe2x95x90CHR, wherein R is a C1-C10 alkyl radical, optionally containing minor proportions of polyenes units. The saturated elastomeric copolymers obtainable with the catalysts of the present invention contain from 15 to 85 mol % of ethylene units, the complement to 100% consisting of units of one or more xcex1-olefins and/or of a non-conjugated diolefin able to cyclopolymerize. The unsaturated elastomeric copolymers also contain, in addition to the units deriving from the polymerisation of ethylene and xcex1-olefins, minor proportions of unsaturated units deriving from the copolymerization of one or more polyenes. The content of unsaturated units can vary from 0.1 to 5% by moles and it is preferably comprised between 0.2 and 2% by moles.
The elastomeric copolymers obtainable with the catalysts of the invention are endowed with valuable properties, such as a low content of ashes and uniformity of distribution of the comonomers along the copolymeric chain.
The xcex1-olefins which can be used as comonomers in the elastomeric copolymers comprise propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene.
Polyenes which can be used in elastomeric copolymers comprise:
polyenes able to give unsaturated units, such as:
linear, non-conjugated dienes such as 1,4-hexadiene trans, 1,4-hexadiene cis, 6-methyl-1,5-heptadiene, 3,7-dimethyl-1,6-octadiene, 11-methyl-1,10-dodecadiene;
monocyclic diolefins such as, for example, cis-1,5-cyclooctadiene and 5-methyl-1,5-cyclooctadiene;
bicyclic diolefins such as for example 4,5,8,9-tetrahydroindene and 6 and/or 7-methyl-4,5,8,9-tetrahydroindene;
alkenyl or alkyliden norbornenes such as for example, 5-ethyliden-2-norbornene, 5-isopropyliden-2-norbornene, exo-5-isopropenyl-2-norbornene, 5-vinyl-2-norbornene;
polycyclic diolefins such as, for example, dicyclopentadiene, tricyclo-[6.2.1.02.7]4,9-undecadiene and the 4-methyl derivative thereof;
non-conjugated diolefins able to cyclopolymerize, such as 1,5-hexadiene, 1,6-heptadiene, 2-methyl-1,5-hexadiene; conjugated dienes, such as butadiene, 1,3-pentadiene and isoprene.
A furter interesting use of the catalysts according to the present invention is in the preparation of cycloolefin polymers. Monocyclic and polycyclic olefin monomers can be either homopolymerized or copolymerized, also with linear olefin monomers. Non limitative examples of cycloolefin polymers which can be prepared with the catalysts of the present invention are described in the European patent applications EP-501,370 and EP-407,870.
The polymerisation processes of the present invention can be carried out in liquid phase, optionally in the presence of inert hydrocarbon solvents, or in gas phase. Said hydrocarbon solvent can be either aromatic (such as toluene) or aliphatic (such as propane, hexane, heptane, isobutane, cyclohexane and 2,2,4-trimethylpentane).
The polymerisation temperature generally ranges from about 0xc2x0 C. to about 250xc2x0 C. In particular, in the processes for the preparation of HDPE and LLDPE, it is preferably comprised between 20xc2x0 C. and 150xc2x0 C. and, more preferably between 40xc2x0 C. and 90xc2x0 C., whereas for the preparation of elastomeric copolymers it is preferably comprised between 0xc2x0 C. and 200xc2x0 C. and, more preferably between 20xc2x0 C. and 100xc2x0 C.
The molecular weight of polymers can be varied simply by varying the polymerisation temperature, the type or the concentration of the catalyst components, or by using molecular weight regulators, such as hydrogen.
The molecular weight distribution can be varied by using mixtures of different cyclopentadienyl compounds or by carrying out the polymerisation in several stages which differ in the polymerisation temperature and/or the concentrations of molecular weight regulator. The polymerisation yield depends on the purity of the metallocene components in the catalyst. Therefore the metallocene obtained by the process of the invention may be used as such, or subjected to purification treatments.